Rechargeable battery with gas release safety vent

ABSTRACT

A rechargeable battery including an electrode assembly containing a positive electrode, a negative electrode and a separator interposed therebetween, a case having a space for housing the electrode assembly therein, lead elements connected to the electrode assembly and disposed at a sealing region of the case, and a sealant arranged between and adjacent to the case and the lead element the sealant including an area having relatively less resistance to fracture.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2005-0034389 filed in the Korean IntellectualProperty Office on Apr. 26, 2005, the entire content of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a rechargeable battery having animproved safety vent for releasing gases generated in the battery.

BACKGROUND OF THE INVENTION

Unlike non-rechargeable batteries, rechargeable batteries may berecharged. Non-aqueous electrolyte rechargeable batteries with highenergy density have recently been developed as high power rechargeablebatteries.

Lower power batteries in which battery cells are made into a batterypack are used as a power source for various portable electronic devicessuch as cellular phones, laptop computers, and camcorders. Largerbattery packs which are formed by connecting several to tens ofrechargeable battery cells may be suitable for motor driven devices suchas electric vehicles.

Rechargeable batteries may be classified into different categories basedon their external shape, for example pouch-type, cylindrical, andprismatic shapes. The pouch-type case battery has been used in slim andlight-weight portable electronic devices due to its flexible shape andlight weight.

Unlike cylindrical or prismatic rechargeable batteries with cases thatare formed of a relatively thick metal, pouch-type rechargeablebatteries have a case formed of a thin metal film with insulating filmsattached at both sides thereof so that the battery is flexible. Thepouch-type case has a space for housing the electrode assembly, andclosing and sealing parts for heat-sealing along the edge of the space.

The conventional rechargeable battery may explode due to gas generationwhen its internal voltage increases due to overcharging. Particularly, alithium ion battery may have increased internal pressure caused byreleased gas, such as carbon dioxide, carbon monoxide, and the like,when a liquid electrolyte is decomposed due to an overcharge. Inaddition, the battery may catch fire when the internal temperature ofthe battery increases due to over-current caused by an over-discharge orover-charge.

In general, a rechargeable battery can be used safely only whentemperature requirements both at charge and during operation are met.However, when a temperature at battery charge or discharge, or duringbattery operation in machinery or equipment, is too high, theunfavorable external temperature condition may cause the batterytemperature to increase, leading to explosion or combustion of thebattery.

Therefore, a rechargeable battery should pass various safety tests as tohigh temperature storage, thermal shock, temperature storage, and thelike before it is distributed for sale. These safety tests are performedby leaving the battery in various temperature conditions for variouslengths of time. Batteries should not explode or catch fire to pass thetests and may be unsealed to prevent explosion or combustion in extremesituations.

There have been various attempts to make secondary batteries safer.Particularly, much attention has been paid to technology for eliminatinginternal gas by equipping a safety vent on a battery case. Accordingly,a can-type battery using a prismatic or cylindrical can as a batterycase is mounted with a safety vent having such a structure at a capplate or at the can itself so that the battery cannot be destroyed whenthe internal temperature or pressure increases. However, unlike can-typebatteries, pouch-type rechargeable batteries have not been able to bemounted with a safety vent, because their case is formed of a flexiblematerial.

SUMMARY OF THE INVENTION

An exemplary embodiment of the present invention provides a pouch-typerechargeable battery having a safety vent that can be simplymanufactured and easily mounted.

According to an embodiment of the present invention, a rechargeablebattery is provided that includes an electrode assembly containing apositive electrode, a negative electrode, and a separator interposedtherebetween, a case having a space for housing the electrode assemblytherein, lead elements connected to the electrode assembly and disposedat a sealing region of the case, and a sealant arranged between andadjacent to the case and each lead element, a portion of the sealanthaving a relatively weaker breaking strength.

The case may be a pouch, and the sealant may be mounted with the leadelements. The sealant may include at least one area that is thinner thanthe rest of the sealant. The sealant may include at least one groove.The grooves are not limited to a particular shape, but can be formed asnotches. In addition, more than two grooves may be formed in oppositedirections.

The sealant may have at least one reduced contact area between the caseand the sealant itself. Here, the sealant may also include at least onenon-contact area when it is closely adjacent to the case. The contactingarea between the sealant and the case may be formed to taper toward thecenter of the sealant. The non-contact area may be formed to taperoutward from the center of the sealant from the point where it contactsthe internal or external side of the case.

The non-contact areas may be arranged to oppose each other at the areawhere the sealant is closely adjacent to the internal end or externalend of the case.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a rechargeable batteryfabricated according to an embodiment of the present invention.

FIG. 2 is a schematic top plan view showing the assembled status of arechargeable battery fabricated according to an embodiment of thepresent invention.

FIG. 3 is a schematic top plan view showing the assembled status of arechargeable battery fabricated according to another embodiment of thepresent invention.

FIG. 4 is a schematic top plan view showing a rechargeable batteryfabricated according to another embodiment of the present invention.

FIG. 5 is a schematic block diagram showing a rechargeable batterydriving a motor according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As shown in FIG. 1, a pouch-type rechargeable battery 10 includes anelectrode assembly 20 formed by interposing a separator 24 between apositive electrode 22 and a negative electrode 23 and then winding themtogether in a jelly-roll configuration, and a case 30 for housing theelectrode assembly 20.

Referring to the drawing, the electrode assembly 20 is formed in aspiral-wound jelly-roll shape after interposing a separator 24 between apositive electrode 22 and a negative electrode 23, but it not limitedthereto. For example, the electrode assembly may be formed as a stack byinterposing a separator 24 between a positive electrode 22 and anegative electrode 23. This alternative structure may be applied to allof the following embodiments without exception.

The electrode assembly 20 includes the positive electrode 22 and thenegative electrode 23 which are electrically connected to lead elements25, 26, respectively.

The lead elements 25, 26 should be long enough to protrude from the case30, and are arranged to be closely adjacent to a sealant 27 at an areacontacting the case 30.

The sealant 27 is formed of an insulating resin and is used to prevent ashort circuit between the case 30 and each lead element 25, 26, and toseal therebetween. According to an embodiment of the present embodiment,the sealant 27 may function as a safety vent, which is illustrated indetail hereafter.

As illustrated in FIG. 1, the electrode assembly 20 is housed in a case30 having a space 33. The case 30 includes a case body 31. formed withthe space 33 and a cover 32 sealing the space 33. The cover 32 is formedto extend from one end of the case body 31 and to join with a flangeformed around the space 33, and to form a sealing region 34 as shown inFIG. 2.

The shape of the case 30 is not limited to the aforementioned shape, butmay also be formed as a pouch with an opening at one end for housing anelectrode assembly and being sealed, even though this is notillustrated.

The case 30 may be formed of a thin plate having a mixture of a metaland a resin. The thin plate is formed of a composite made by includingan internal thermal adhesive layer comprising a polymer resin, forexample, modified polypropylene and the like, and an exterior resin suchas nylon or polyethylene terephthalate, and then pressing them together.

Accordingly, the case 30 may be sealed by hot-pressure when the thermaladhesive layers of the case body 31 and the cover 32 are positioned toface each other.

The case 30 is sealed by forming a sealing region 34 along a flange ofthe case body 31. The sealing region is formed by thermally bonding thecase body 31 with the cover 32 after the electrode assembly 20 isinserted into the case 30. The sealing region 34 has two lead elements25, 26 protruding therefrom, and connected with a positive electrode 22and a negative electrode 23 of the electrode assembly 20. The sealant 27attached to each lead element 25, 26 is positioned to contact a part ofthe sealing region 34. The sealant 27 joins with the sealing region 34of the case 30, maintaining air-tightness between the case 30 and thelead elements 25, 26 when the case is not pressure sealed.

As illustrated in FIG. 2, the sealant 27 may be mounted in such a waythat two ends of the sealant are outwardly exposed from the sealingregion 34 in the lengthwise direction of the lead elements 25, 26.Otherwise, the two ends of the sealant 27 would not be long enough toextend from the sealing region 34.

According to an embodiment of the present invention, the sealant 27 mayinclude at least one area contacting the case 30, such as area “A,” withless resistance to fracture than the rest of the sealing region 34. Thearea with less resistance to fracture may act as a safety vent whichruptures to secure battery safety when the internal pressure of thebattery increases.

The area with less resistance to fracture may be formed by regulatingthe thickness of the sealant 27 or the area where the sealant 27 isadjacent to the case 30.

According to one embodiment of the present invention, the sealant 27 mayhave at least one groove toward the center of the case 30 in acontacting area “A,” where the sealant 27 forms part of the sealingregion 34 with the case 30.

The sealant 27 has less surface area contact with the case 30 at thegroove less than at the other areas, and accordingly it has lessresistance to fracture at the groove. When the internal pressure of abattery increases, the area ruptures to release gas inside the case 30.Here, the sealant 27 may have various rupture pressures depending on thedepth of the groove, but the depth of the groove has no particularlimit.

The sealant 27 can include two substantially identical grooves opposingeach other at the internal and external adhesive sides of the case 30.

The groove has no particular limit to its shape, but it may be formed asa notch 28. The notch 28 denotes a place where the width of the sealant27 sharply decreases in a lengthwise direction of the lead elements 25,26. According to the embodiment of the present invention, the notch 28may be shaped as a letter “V” with its tip pointing toward the center ofthe sealant.

As shown in FIG. 2, the sealant 27 has a notch 28 at the contacting area“A” with the case 30, where the sealant forms part of the sealing region34, and so has a width that is reduced by the notch 28. Accordingly thesealant 27 has less resistance to fracture at the notch 28 than theother areas.

When the rechargeable battery 10 mounted with a sealant 27 having thenotch 28 internally produces gas due to over-charge/over-discharge orhigh temperature usage, thus increasing the internal pressure of thebattery, the case 30 expands. The sealant 27 then ruptures at the notch28 due to concentrated stresses as the internal pressure increases.Internal gas of the battery is then released through the ruptured notch28, preventing explosion or combustion of the battery.

According to another embodiment of the present invention, the groove maybe formed as a circular arc 28′ as shown in FIG. 3. In FIG. 3, the samemembers that are the same as members in FIG. 2 are assigned the samereference numerals as in FIG. 2.

FIG. 4 schematically shows a rechargeable battery 10 fabricatedaccording to another embodiment of the present invention. Therechargeable battery 10 includes an electrode assembly 20 having apositive electrode and a negative electrode with a separator interposedtherebetween, lead elements 25, 26 electrically connected with thepositive and negative electrodes, respectively, a case 30 having a spacefor housing the electrode assembly 20, comparable to that previouslydescribed with respect to FIG. 1. The case 30 is sealed with the leadelements 25, 26 outwardly exposed, and a sealant 29 ensures that thelead elements 25, 26 are adjacent to the case 30. The sealant 29 mayinclude at least one non-contact area “N” at the contacting area “A”with the case 30. As illustrated in FIG. 4, the non-contact area “N” isformed at the inner side or the outer side of the case 30.

The non-contact area “N” is formed between the sealant 29 and thesealing region 34 of the case 30. The non-contact area “N” may be formedas a notch toward the center of the sealant 29-at the internal side ofthe case 30. The notch-type non-contact area “N” may have a “V” shape.

In addition, the non-contact areas “N” may be formed toward the centerof the sealant 29 from the internal and external sides of the case 30.They may face each other and have substantially the same size.

Since the sealant 29 has less contact area with the case 30 than therest of the sealing region 34 due to the non-contact area “N,” it mayrupture due to concentrated stresses at the non-contact areas “N” causedby increased internal pressure of the battery.

The sealant 29 may have various rupture pressures depending on thenon-contact areas “N” formed therein, but there is no particular limitto the area thereof.

The non-contact area “N” may be formed at the contacting area “A”between the sealant 29 and the sealing region 34 of the case 30. Forexample, after fabricating a press that hot-presses the sealant 29 andthe sealing region 34 of the case to form a groove shape correspondingto the non-contact area “N”, the non-contact area “N” may be formed as agroove shape where the sealant is not closely adjacent to the case 30.Of course, the non-contact area may be formed in various ways other thanthe above example, according to the general scope of the presentinvention.

The present invention provides improved sealants 27, 29 mounted withlead elements 25, 26, allowing the sealants 27, 29 to work as safetyvents to release internal gas inside a battery when it isover-pressurized.

The rechargeable battery may be used as an energy source for driving amotor for a hybrid electric vehicle (HEV), an electric vehicle (EV), acordless cleaner, a motorbike, an electric scooter, and the like as wellas small-sized electrical equipment.

A plurality of the above-mentioned rechargeable batteries are connectedto each other in series or in parallel to provide a battery module. FIG.5 is a schematic block diagram of a battery module 1 which includes therechargeable batteries as discussed in FIGS. 1 to 4 for driving a motor50.

In this way, a rechargeable battery fabricated according to the presentinvention can prevent thermal runaway or combustion and explosion byappropriately releasing internal gas, thereby securing safety andreliability.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, rather is intended to cover various modifications andequivalent arrangements included within the spirit and scope of theappended claims.

1. A rechargeable battery comprising: an electrode assembly having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; a case having a space for housing the electrode assembly; a plurality of lead elements connected to the electrode assembly and protruding from the case at a sealing region of the case; and a sealant arranged between and adjacent to the case and each lead element at the sealing region, the sealant having an area of relatively less resistance to fracture.
 2. The rechargeable battery of claim 1, wherein the case is a pouch.
 3. The rechargeable battery of claim 1, wherein the sealant has at least one groove formed along the lengthwise direction of the plurality of lead elements.
 4. The rechargeable battery of claim 3, wherein the at least one groove is shaped as a notch.
 5. The rechargeable battery of claim 3, wherein at least two grooves are formed facing each other.
 6. The rechargeable battery of claim 1, wherein the sealant includes at least one contact area having a reduced width within the sealing region for sealing the sealant with the case.
 7. The rechargeable battery of claim 6, wherein the sealant includes at least one non-contact area adjacent to the contacting area.
 8. The rechargeable battery of claim 6, wherein the width of the contact area decreases toward the center of the sealant.
 9. The rechargeable battery of claim 7, wherein the non-contact area is formed as a circular arc.
 10. The rechargeable battery of claim 7, wherein the non-contact area has a pointed end toward the internal end of the sealant.
 11. The rechargeable battery of claim 1, wherein the rechargeable battery drives a motor.
 12. A method for safety venting a rechargeable battery, the rechargeable battery having an electrode assembly within a case, the case having an upper portion and a lower portion sealed at a sealing region at the periphery of and between the upper portion and the lower portion, the method comprising: mounting the electrode assembly within the case such that electrodes of the electrode assembly protrude from the case at the sealing region; and locating a sealant on the electrodes at the sealing region, the sealant having an area rupturable when internal pressure within the rechargeable battery reaches a predetermined rupture pressure.
 13. The method of claim 12, wherein the area rupturable is formed by a plurality of grooves tapering toward the interior of the sealant.
 14. The method of claim 12, wherein the case is a pouch.
 15. A rechargeable battery comprising: an electrode assembly having a plurality of protruding electrodes; a case having an upper portion and a lower portion, the lower portion having a space for mounting the electrode assembly, the case having a sealing region at the periphery of and between each of the upper portion and the lower portion; and a sealant located on the protruding electrode at the sealing region, the sealant having an area ruptureable when the upper portion and the lower portion are sealed at the sealing region and when internal pressure within the battery reaches a predetermined rupture pressure.
 16. The rechargeable battery of claim 15, wherein the area rupturable is formed by a plurality of grooves tapering toward the interior of the sealant.
 17. The rechargeable battery of claim 15, wherein the case is a pouch. 